Re: [PATCH v2 3/3] docs/s390x: document vfio-ccw

[Cornelia Huck <cohuck@redhat.com>]

On Sun, 17 May 2020 19:52:43 +0200
Thomas Huth <thuth@redhat.com> wrote:

> On 15/05/2020 17.15, Cornelia Huck wrote:
> > Add a basic example for passing a dasd via vfio-ccw.
> > 
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> >  docs/system/s390x/vfio-ccw.rst | 72 ++++++++++++++++++++++++++++++++++
> >  docs/system/target-s390x.rst   |  1 +
> >  2 files changed, 73 insertions(+)
> >  create mode 100644 docs/system/s390x/vfio-ccw.rst
> > 
> > diff --git a/docs/system/s390x/vfio-ccw.rst b/docs/system/s390x/vfio-ccw.rst
> > new file mode 100644
> > index 000000000000..4cfd22c3b789
> > --- /dev/null
> > +++ b/docs/system/s390x/vfio-ccw.rst
> > @@ -0,0 +1,72 @@
> > +Subchannel passthrough via vfio-ccw
> > +===================================
> > +
> > +vfio-ccw (based upon the mediated vfio device infrastructure) allows to
> > +make certain I/O subchannels and their devices available to a guest. The
> > +host will not interact with those subchannels/devices any more.
> > +
> > +Note that while vfio-ccw should work with most non-QDIO devices, only ECKD
> > +DASDs have really been tested.
> > +
> > +Example configuration
> > +---------------------
> > +
> > +Step 1: configure the host device
> > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > +
> > +Note: it is recommended to use the ``mdevctl`` tool for this step.
> > +
> > +To define the same device as configured below to be started
> > +automatically, use
> > +
> > +::
> > +
> > +   [root@host ~]# driverctl -b css set-override 0.0.0313 vfio_ccw
> > +   [root@host ~]# mdevctl define -u 7e270a25-e163-4922-af60-757fc8ed48c6\
> > +                  -p 0.0.0313 -t vfio-ccw_io -a
> > +
> > +If this is not possible or wanted, follow the manual procedure below.
> > +
> > +* Locate the subchannel for the device (in this example, ``0.0.2b09``)::
> > +
> > +    [root@host ~]# lscss | grep 0.0.2b09 | awk '{print $2}'
> > +    0.0.0313
> > +
> > +* Unbind the subchannel (in this example, ``0.0.0313``) from the standard
> > +  I/O subchannel driver and bind it to the vfio-ccw driver::
> > +
> > +    [root@host ~]# echo 0.0.0313 > /sys/bus/css/devices/0.0.0313/driver/unbind
> > +    [root@host ~]# echo 0.0.0313 > /sys/bus/css/drivers/vfio_ccw/bind
> > +
> > +* Create the mediated device (identified by a uuid)::
> > +
> > +    [root@host ~]# uuidgen
> > +    7e270a25-e163-4922-af60-757fc8ed48c6  
> 
> Maybe the uuidgen lines should now be moved before the mdevctl example
> already, so that it is already clear there where the uuid comes from?

Yeah, makes sense.